Firing of a fuel or a monofuel

ABSTRACT

To initiate liquid-fuel combustion or monofuel decomposition, and particularly to operate an impact cylinder by a fuel without requiring a spark or hot point, part of the fuel for each stroke is injected into a firing breech containing a gas and sealingly cooperating with a firing pin which when released by a trigger fires this fuel by compression of the gas in the breech to reach firing pressure and temperature, the resultant pressure increase being utilized for opening communication from the breech to a main reaction chamber into which the remainder of the fuel has been injected and also for recocking the firing pin.

United States Patent lnventor Appl. No, Filed Patented Assignee Priority Peter B. Kahn llford, Essex, England 814,891

Apr. 3, 1969 Apr. 27, 1971 The Plessey Company Limited lliord, England Apr. 4, 1968, Feb. 27, 1969 Great Britain 16216/68 and 10476/69 name or A FUEL OR A MONOFUEL Primary Exdminer-Wendell E. Burns Attorney-Blum, Moscovitz, Friedman & Kaplan ABSTRACT: To initiate liquid-fuel combustion or monofuel decomposition, and particularly to operate an impact cylinder by a fuel without requiring a spark or hot point, part of the fuel for each stroke is injected into a tiring breech containing a gas and sealingly cooperating with a firing pin which when released by a trigger fires this fuel by compression of the gas in the breech to reach firing pressure and temperature, the resultant pressure increase being utilized for opening communication from the breech to a main reaction chamber into which the remainder of the fuel has been injected and also for recocking the firing pin.

FllRlNG or A FUEL on A MONOFUEL This invention relates to the initiation of a chemical reaction in which a fuel, which may be a monofuel, is utilized to produce a hot gas mixture under pressure. Such reaction may be the combustion of an ordinary fuel, particularly a liquid fuel, or the decomposition of a monofuel, and hereinafter the term fuel, unless the context otherwise requires, is intended to include monofuel. A monofuel, also known as a monopropellant (a term used for example in U.S. Pat. No. 2,947,221), is a substance capable of developing heat by an internal reaction not requiring the presence of oxygen, and the below-mentioned isopropyl nitrate is one example of a monofuel or a monopropellant. In both cases the initiation of the reaction, also referred to as the firing of the fuel, requires the temperature of the fuel to be raised, at least locally, to a predetermined minimum temperature also referred to as the firing point, and the present invention has for an object to provide an improved system and apparatus for achieving this without the need of providing either an electric spark or a solid body raised to incandescent temperature. A further object is to provide a firing device for a fuel-and-gas mixture, in which on the one hand firing is effected by adiabatic compression of a gas to which the fuel has been added while on the other hand the pressure rise subsequent to the firing is kept relatively low so as to avoid the need of an excessively heavy construction of the device.

According to a broad aspect of the invention, which can be applied both to the firing of a monofuel in the presence of a gas which may be inert and to the firing of a mixture of other fuel with air or other oxygen-containing gas, a breech is charged with the fuel in the presence of the gas, and the fuelandgas mixture in the breech is then compressed, to establish spontaneous-firing conditions, by a spring-loaded piston element, hereinafter called a firing pin, released by trigger action and free to be moved back after the firing by the increased breech pressure resulting from the firing, and preferably arranged to be recocked by this return movement. Thus the volume increase of the firing chamber after ignition is not, as in a diesel engine, limited by an element, such as a piston connected to a crankshaft, whose movement is predetermined, in practice according to a steady cycle, since the firing pin will give way with very little inertia to the pressure resulting from the firing, thereby avoiding an excessive sudden increase in pressure.

In a more specific aspect of the present invention a metered quantity of a liquid monofuel, for example isopropyl nitrate is, in a cocking operation, transferred from a reservoir into a breech and the monofuel in the breech is then fired by compressing the gas in the breech by the rapid movement of a spring-loaded piston or plunger which may be referred to as firing pin, when the firing pin is released by trigger action from a cocked position, the firing pin being, immediately after firing, forced back and thus cocked for the next firing operation by the breech pressure of the decomposing monofuel. The breech is further provided with a port which, immediately after the firing, establishes communication between the breech and a further portion of the reaction chamber. To achieve this, the return movement of the firing pin may open the breech to a main portion of the reaction chamber, in which before the firing the mixture of gas and fuel or monofuel is under a pressure substantially lower than the firing pressure. The increase in pressure and temperature due to the admission of the fired gases from the breech then causes the mixture in said main part of the reaction chamber to be also fired. The power of the decomposing monofuel may be used to operate an impact piston which operates against a thrust spring, by which the piston is, after each firing, returned to its starting position, an atmospheric vent port being preferably provided to vent the decomposition chamber at the end of each operating stroke. Charging or priming of the reaction chamber, which in this case may also be called the decomposition chamber, with liquid monofuel from a monofuel reservoir is preferably effected by manual forward movement and subsequent spring-actuated return of a pump piston in a pump cylinder communicating through nonretum valves with the reservoir and the decomposition chamber. In order to permit ready adjustment of the quantity of monofuel injected to match the desired impact, an adjustment end stop for the piston stroke is preferably combined with the priming pump, whose piston is preferably arranged to aspire monofuel from the reservoir during its manually effected inward stroke while a return spring is compressed and to expel the same amount of monofuel from the priming-pump cylinder during the spring-operated return stroke via the passage in the piston which contains a nonretum valve and which at the end of the return stroke communicates with an atmospheric port so as to prevent reliably the transmission of any pressure from the decomposition chamber past the nonretum valves in the delivery line and in the reservoir line to the monofuel reser- VOlI'.

Alternatively the reaction chamber may, if desired, be arranged to deliver gas to a gas turbine, more particularly to a starter gas turbine. In that case monofuel is after the firing continued to be fed to the reaction chamber at a steady rate for as long as the starter turbine is required to be operated.

In order that the invention may be more readily understood, a number of examples will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates one form of a firing system for monofuel shown in axial section, together with a single-stroke piston intended to be operated by the decomposition gases, and with a charging and/or priming pump,

FIG. 2 is an axial section of another form of monofueloperated piston device constructed according to the invention,

HO. 3 is an axial section of a priming pump for use therewith, and

FIG. 4 is an axial section, drawn to a larger scale, of the inlet valve provided with back pressure protection means.

Referring new first to FIG. 1, the illustrated device comprises a cylinder barrel 1 having a cylinder bore 5 in which an impact or working piston 6 having a piston rod 8 is slidably movable from its illustrated normal position against a return spring 7. ln use the piston is actuated by monofuel-decomposition gas produced in a cylindrical reaction chamber 17 coaxial with, but separated by a partition 14 from, the cylinder bore 5, decomposition gas being admitted from the reaction chamber to the end of the cylinder bore 5 by a passage 15 in the partition 14. The reaction chamber 17 is extended in the axial direction of the barrel 1 by a breech 16 of smaller diameter, and arranged slidably in the chamber 17 is a precompressor piston 21, from which a cylindrical plunger 18, hereinafter referred to as a firing pin, projects towards the breech 16, in alignment with the latter, so as to be movable into the breech, in which it is a sealing fit. The precompressor piston 21 is illustrated in its cocked position, in which a helical firing spring 19 is axially compressed, and in which the piston 21 is retained by a detent or sear 22, which is releasable by a trigger lever 20 at this time the reaction chamber 17 and the breech 16 are filled with a gaseous fluid, which may be air or the gaseous products of a preceding operation. The cocking and trigger means may be of any known or suitable construction, for example be as described in U.S. Pat. No. 3,366,058. When it is intended to operate the working piston 6 by monofuel-decomposition gas, a suitable quantity of liquid monofuel, for example of isopropyl nitrate, is fed from the reservoir 3 into the reaction chamber 17 by a priming pump 4. This pump is arranged to meter, in a first part of its operative stroke, a preselected quantity of monofuel into the reaction chamber 17 proper by a line 39, and to deliver, near the end of its operative stroke, a fixed small further quantity of monofuel into the breech 16 by a second line 40. When now the precompressor piston 21 is released upon actuation of the trigger 20, the helical spring 19 moves the precompressor piston rapidly forward to increase the pressure of the gas contained in the reaction chamber 17 and, after a suitably increased pressure has been reached in this chamber, the firing pin 18 enters the breech 16, thereby sealing a quantity of the thus precompressed gas in the breech 16, whose residual length is considerably less than the remaining length of the reaction chamber 17. Further movement of the precompressor piston 21 and its firing pin 18 will therefore cause, during the following part of the movement of piston 21 the pressure in the breech 16 to rise much more rapidly than that in the chamber 17. Owing to the small cross-sectional area of the breech 16 compared to that of the reaction chamber 17, this final part of the forward movement of the piston structure 21, 18, which by this time has acquired a considerable kinetic energy, will cause the pressure and temperature in the breech 16 to rise rapidly to reach the firing point. The resultant decomposition of monofuel cause the pressure in the breech to rise further very sharply, and as a result the firing pin is thrown back at a high velocity to acquire an ener gy sufiicient to return, assisted by the pressure in the reaction chamber, the precompressor piston 21 to its illustrated position, where it is once more retained by the detent 22. As soon as, during this return movement, the firing pin 18 leaves the breech 16, the decomposition gases from the breech enter the main reaction chamber 17, where the resulting increase in pressure and temperature initiates decomposition of the monofuel contained in that chamber. A high pressure will thus be created in the reaction chamber 17, though this pressure will not be as high as that momentarily developed in the breech, because the initial compression of the gases in chamber 17 is lower than that reached in the breech at the moment of spontaneous firing. This reaction-chamber pressure acts, through a passage 15, on the area of an annular recess of the working piston 6, and when the pressure acting on this area is high enough to overcome the force of the return spring 7, the impact or working piston 6 begins to move away from the partition 14 which separates the cylinder 5 from the reaction chamber 17, thus allowing the reactionchamber pressure to reach the whole area of the working piston 6. This piston is thus given a high rate of acceleration to reach a high speed which may be utilized in an impact tool in any known or convenient manner.

The priming pump 4 comprises a piston rod 23 equipped with a stepped pump piston 26. The latter slides in a pump cylinder 25 and is urged by a bias spring 27 towards the illustrated end position. When it is desired to prime the system, the pump piston 26 is moved against the bias spring 27 by pressing a knob 24 mounted on the end of the piston rod 23. This inward stroke of the pump piston 26 is limited by abutment of an adjustable stop nut 33 against the end of the pump cylinder 25, adjustment of the knob serving to determine the amount of monofuel injected at each reciprocation in accordance with the momentary requirements of the system. The pump cylinder 25 has three apertures or ports 28, 29 and 29a, of which the first-mentioned aperture 28 communicates with the monofuel reservoir 3 through a nonreturn valve 35, while the apertures 29 and 29a lead respectively through line 39 to the main reaction chamber 17 and through line 40 to the firing breech 16, each of the lines 39 and 40 being fitted with a nonretum valve 37 and 37a respectively. A longitudinal passage 31 is provided in the pump piston 26 and the piston rod 23 and communicates with three radial ports 32, 33 and 33a. The first-mentioned port 32 permanently communicates with the first-mentioned pump-cylinder port 28 through the end portion 25a of the bore of pump cylinder 25, while the other two ports 33 and 33a of the piston 26 respectively communicate with longitudinal channels 36 and 360 at the circumference of the pump piston 26 in such manner that, when the pump piston 26 returns to its illustrated position after the knob 24 has been depressed, channel 36 first allows monofuel displaced by the piston from the said end chamber 250 of the cylinder 25 to flow to the main decomposition chamber 17 while, from a predetermined point shortly before the end of the return stroke of the pump piston the channel 36 leaves the second cylinder pon 29 but the other channel 36a begins to communicate with the third cylinder port 29a thus ensuring that, irrespective of the amount of work requiredto be done by the decomposition products. The firing breech 16' is always fed with a metered quantity of monofuel suitable to ensure optimum firing conditions, while variation of the power output of the device is achieved by varying the amount of monofuel fed to the main reaction chamber 17.

It will be readily appreciated that, while the invention has been described as applied to an impact piston, the same principle of operation can also be applied to other uses, for example for initiating the operation of a continuously operating device such as a starter gas turbine. For this purpose the piston 6 may be constructed as, or replaced by, a pressurizing valve which remains closed until the pressure in the reaction chamber 17 reaches a predetermined value, and an additional fuel pump, suitable to provide a continuous steady supply of monofuel to the reaction chamber 17, is provided and arranged to commence operation when, or shortly before the piston 21 and firing pin 18 is released to initiate monofuel decomposition in the breech 26.

When it is required to replenish the monofuel in the reservoir 3, this can be done by opening a lateral cover 41 provided for the purpose. Finally it will be appreciated that, while the invention is mainly intended for use with monofuel such as isopropyl nitrate, it is also capable of being operated with fuels requiring oxygen for combustion, for example with petrol or with diesel oil, provided that in that case arrangements are made to ensure for each operation the presence of combustion-sustaining gas, generally air, in the reaction chamber 17 at a suitable quantitative ratio to the monofuel.

Another embodiment of the invention is illustrated in FIGS. 2 to 4, in which the same reference numbers as in FIG. 1 have been employed for parts performing the same functions.

Referring now to FIG. 2, and concentrating on the features which differ from those of FIG. 1, it will be noticed that the firing pin 18, instead of being attached to a precompression piston as that shown at 21 in FIG. 1, is attached to a guide rod 43 provided with a spring abutment head 42, on which the spring 19 acts, and which is freely movable in a vented bore 71. The movement of the head 42 is so limited by a shoulder 44 on its guide rod 43 that the end of the firing pin 18 remains permanently engaged in a breech 45 which latter, like the breech 16 of FIG. 1, is formed in the partition 14 that forms the end wall of the working cylinder 5; but in contrast to the construction of FIG. 1, the breech 45 is formed as a through bore. As a means for retaining the firing pin in the cocked position, a simple spring-loaded trigger pin 32 is shown, which however may, if desired, be equipped with means which ensure its reengagement as soon as the firing pin 18 and springabutment head 42 return to the illustrated position after firing.

The guide rod 43 is adapted, as shown, to be manually withdrawn to enable the firing pin 18 to be cocked manually when it has been released in the absence of a charge. The spring-loaded piston 6 is formed with a central boss 46 which, when the piston is held in its illustrated end position by the spring 7, seals the exit from the through-bore breech 45 into the cylinder bore 5, which forms the reaction chamber while a peripheral collar 47 of the piston 6 keeps the end surface of the piston slightly spaced from the partition 14 to form an annular chamber 9 surrounding the boss 46. The passage 40 through which the variable greater portion of the monofuel is supplied from the priming pump 4 for the operation of the working piston 6, is arranged to lead into this annular chamber 9 via an inlet check valve 48a and a similar inlet check valve 48 is interposed in the passage 39 which feeds an invariable small quantity of monofuel into the breech 45 for firing purposes. As will be seen in FIG. 4, the housing of the inlet valve 48 is provided, to the back of its valve seat 49, with a crossbore 50 intersecting the flow passage 51 leading to the valve seat 49, and this cross-bore 50 is normally closed by a burster disc 52. Should for any reason the valve fail to prevent back pressure from the firing breech 45 or from the pressurized end of the cylinder bore 5 from reaching the passage 51, which is isolated from the monofuel reservoir by one of the delivery valves 37 and 37a of the priming pump 4, the resultant pressure buildup in the passage 51 will burst the disc 52, thus venting the passage 51 to a point at low pressure and avoiding any risk of transmission of firing pressure back to the monofuel reservoir.

Referring now to the construction of the priming pump illustrated in FIG. 3, it will be noticed that this pump has been modified from that shown in FIG. 1. Thus the actuating knob 34 of the construction of FIG. 3 combines the functions of the actuating knob 24 and of the adjuster nut 38 of FIG. 1, and instead of arranging for a single pump piston 26 to feed in succession first a variable quantity of monofuel to the main reaction chamber and then a smaller, fixed quantity to the breech, the single piston 26 has been replaced by a main pump piston 52, which serves for the supply of monofuel by a line 40 to the annular chamber 9 surrounding the boss 46 of the working piston 6, and this main piston 52 has a coaxial bore 53, in which an auxiliary piston 54 is movable relative to the main piston 52 between a normal position, to which the auxiliary piston is urged by a spring 55, and in which the auxiliary piston 54 is arrested by engagement of a pin 56, projecting from the main piston into a groove 57 of the auxiliary piston, with the end of that groove, and a second position, in which a shoulder 58 of the piston rod 23 terminates the inward movement of the auxiliary piston 54 into the coaxial bore 53. Fuel from the monofuel reservoir is admitted by the inlet valve 35 to an annular chamber 59 which surrounds the pump-piston rod 23 and which communicates, via intersecting bores 60, 61 and a check valve 62, with the bore 53 containing the auxiliary piston 54 and, via a bore 63 and a longitudinal groove 64 in the main piston 52, with the delivery valve 37 which, via line 39, leads to the breech 45. The preloading of the spring 27, which holds the main pump piston 52 in its normal position, is so chosen as to retain when, by pressing the actuating knob 34, the piston rod 23 is moved, the main piston 52 until the auxiliary piston 54 has completed its full permitted stoke thus delivering a predetermined quantity of monofuel to the breech chamber 45. Continued inward movement of the knob 34 then causes the main piston 52 to move jointly with the continued forward movement of the auxiliary piston 54, thereby increasing the capacity of the annular chamber 59 surrounding the piston rod 23 and thus aspiring monofuel from the reservoir through the inlet valve 35. When the knob 34 is now released, the spring 27 will return the main pump piston 52, and the spring 55 will at the same time return the auxiliary piston 54 to its original position relative to the main piston thus causing initially monofuel from the annular chamber 59 to be transferred to the bore 53 constituting the auxiliary cylinder in which the auxiliary piston works, and when this auxiliary cylinder has been fully charged, continued return movement of the main piston 52 will cause the residue of the aspired monofuel to be expelled via delivery valve 37a and line 40 to the annular chamber 9 which constitutes the reaction chamber in the main cylinder bore 5 of the barrel 1. It will be observed that in this manner the charging of the breech is effected during the depression of the knob 34 while the annular chamber 9 is charged during the return movement of the knob 34 and piston rod 23.

When the auxiliary piston 54 has returned to its initial position relative to the main pump piston 52 while the latter continues its return movement, some of the fuel expelled from the annular chamber 59 might flow via passages 60, 61, valves 62, cylinder bore 53, and valve 37 into the breech chamber 45, and to prevent this the pressure drop in the two series-conriected nonretum valves 62 and 37 is arranged to be appreciably greater than the pressure drop in the single nonretum valve 370 provided in the line to the main reaction chamber 9.

When, after the priming pump 4 has been operated, the trigger pin 32 is pulled, the cocking spring 19 is freed to propel the firing pin 18 rapidly into the breech 45 to compress the gas contained therein until the pressure and temperature in the breech causes the monofuel in the breech to decompose spontaneously. The resulting pressure rise in the breech 45 not only moves the firing pin back, cocking it for a fresh firing operation, but also acts on the boss 46 of the working piston 6 to move the boss out of the breech 45, thus establishing communication of the breech with the main reaction chamber 9, so as to tire the main quantity of monofuel which has been fed to the reaction chamber via passage 40. Moreover the pressure of the decomposition gases will now act on the whole area of the piston 6 as distinct from acting only on the area corresponding to the cross section of the boss 46 as it was prior to the establishing of communication between the breech 45 and the annular chamber 9.

The main cylinder 5 is formed with an exhaust port 65 which is exposed when the piston 6 has moved a predetermined distance from its illustrated normal position. This exhaust port 65 will open to atmosphere, as shown, by an atmospheric port 66 when the piston 6 is to work as an impact piston or a reciprocating piston and constitutes the output member, but alternatively, as indicated by the provision of a three-way cock 67, the port 65 may be connected to an output line 68 at which a continuous supply of decomposition gas may be required, for example when as shown the line 68 leads to a gas turbine 69. In order to provide such continuous gas supply, the monofuel supply line 40 leading to the working chamber 9 will, after firing, be connected to a continuous supply source 70 of monofuel, which may be of a construction described in US. Pat. No. 2,874,764 or in US. Pat. No. 3,l46,59l and may, as in these cases, include a gear pump driven by the turbine. The pressure of the decomposition gases will then, as long as the supply of monofuel continues, hold the piston 6 in a position in which it allows the passage of the gases through outlet 65.

lclaim:

1. A device for firing a mixture of a liquid fuel as defined in the specification and a gas, which comprises a body including areaction chamber and a breech bore extending from the reaction chamber and having a substantially smaller diameter than the reaction chamber, said breech bore having a cylindrical portion, first closure means movable longitudinally of the breech bore between a closed position in which said first closure means isolates the breech bore from the reaction chamber and an open position in which it permits free communication between the breech bore and the reaction chamber, spring means urging said first closure means to said closed position, second closure means closing the other end of the breech bore, a firing pin guided in said body for movement along the axis of said breech bore between a first position and a second position said firing pin constituting one of said first and second closure means and including a cylindrical portion which is a sealing fit in said cylindrical bore portion and is movable therein towards the other of said closure means to compress, when rapidly moved from said first position to said second position gaseous fluid in said breech bore sufficiently to ensure firing of such mixture in the breech by adiabatic compression, spring means urging said firing pin to said second position, detent means for releasably holding said firing pin in said first position, detent-release means operable to release said detent means and charging means associated with said body and operable to supply fuel to said reaction chamber and, prior to each release of said detent means, to said breech bore, said body also including conduction means for reaction gases from said reaction chamber to permit such gases to produce mechanical power.

2. A device as claimed in claim 1, wherein the charging means include a single-stoke priming pump arranged to supply fuel to both the breech and the reaction chamber in individually metered quantities.

3. A device as claimed in claim 2, wherein the priming pump includes means for adjusting the quantity of fuel supplied to the reaction chamber without affecting the quantity of fuel supplied to the breech.

4. A device as claimed in claim 1, wherein said body includes a monofuel reservoir associated with said charging means.

firing pin along a path that includes a first position in which said sealing portion is wholly outside said cylindrical bore portion to permit fr'ee communication between said reaction chamber and said breech bore, and a second position in which said sealing portion of the firing pin is in engagement with said cylindrical bore portion so that rapid movement of the firing pin from said first position to said second position will trap a volume of fluid in said breech bore and compress it sufficiently to ensure firing of such mixture in said breech bore. 

2. A device as claimed in claim 1, wherein the charging means include a single-stoke priming pump arranged to supply fuel to both the breech and the reaction chamber in individually metered quantities.
 3. A device as claimed in claim 2, wherein the priming pump includes means for adjusting the quantity of fuel supplied to the reaction chamber without affecting the quantity of fuel supplied to the breech.
 4. A device as claimed in claim 1, wherein said body includes a monofuel reservoir associated with said charging means.
 5. A device as claimed in claim 1, for use in connection with a gas turbine, wherein the charging means include means operable, after the release of the detent means, to direct a continuous supply of fuel to the reaction chamber, the device including a pressurizing valve rendering said conduction means ineffective until the pressure in the reaction chamber reaches a predetermined valve.
 6. A device as claimed in claim 1, wherein the breech bore is a socket bore closed at its end remote from the reaction chamber, and which includes means in said body guiding said firing pin along a path that includes a first position in which said sealing portion is wholly outside said cylindrical bore portion to permit free communication between said reaction chamber and said breech bore, and a second position in which said sealing portion of the firing pin is in engagement with said cylindrical bore portion so that rapid movement of the firing pin from said first position to said second position will trap a volume Of fluid in said breech bore and compress it sufficiently to ensure firing of such mixture in said breech bore. 